This invention relates to a control unit for a machine tool suitable for applying to a machine tool capable of holding a workpiece having a section which is a circular shape and a shape excluding a circular shape.
A recent proposal in order to perform milling machining and turning machining by certainly holding a workpiece which section is a circular shape or an another shape excluding the circular shape is that a plurality of holding members in the shape of a bar is provided at a chuck for holding a workpiece being free to project and drive in the direction of an axial center of the chuck, and a workpiece is held through a plurality of the holding members.
The chuck having such a structure is driven, interlocking the holding members provided at each jaw by oil pressure. When oil pressure is lowered during machining for some reasons, the holding force of a workpiece with the holding members rapidly lowers. Then, a measure desired is that the decrease of oil pressure is detected and a workpiece is properly held till emergency stop of a machine tool.
The object of the present invention is to provide a control unit for a machine tool capable of properly holding a workpiece having various sectional shapes in addition to a workpiece having a circular section even in the case of the decrease of holding force of holding member, such as oil pressure, taking the above-mentioned circumstances into consideration.
The invention of claim 1 is a control unit of a machine tool, said machine tool comprising:
a spindle being rotatable with an axial center as its center
a chuck provided on said spindle;
a plurality of sliding members provided at said chuck, being free to move with respect to said axial center;
workpiece holding members provided at each said sliding member, being free to move and drive with respect to said axial center and being free to be fixed and held;
reciprocating drive means provided at said chuck, being free to drive and reciprocate within a predetermined stroke, thereby being free to move and drive said sliding member in a direction of said axial center; said machine tool having further characteristic:
projecting said workpiece holding members in said axial center direction and driving said reciprocating drive means so a to move said sliding members in said axial center direction when a workpiece is fixed and held with said chuck; said control unit comprising:
a sensor for detecting that the state of said workpiece being fixed and held with said workpiece holding members is released during rotation of said spindle; and
a driving control means of said sliding member for driving and controlling said reciprocating drive means so as to drive said sliding member in said axial center direction when said sensor detects the state of said workpiece being fixed and held with said workpiece holding members is released.
According to the invention of claim 1, the driving control means of the sliding member drives and controls the reciprocating drive means so as to drive the sliding member in the direction of the axial center when the sensor detects that the state of the workpiece fixed and held with the workiece holding members is released during the rotation of the spindle. Then, the decrease of the holding force of the workpiece can be prevented to the utmost by moving the sliding members in the direction of the axial center, that is, in the direction of the workpiece even in the case of decrease of the holding force of the workpiece holding member, such as the oil pressure, thereby the workpiece having various sectional shapes can be properly held in addition to the workpiece having circular section.
The invention of claim 2 is the control unit of the machine tool as set forth in claim 1, wherein said reciprocating drive means has a driving cylinder, being free to reciprocate and drive a rod, and said rod is driven and reciprocated so as to move said sliding member in said axial center direction.
According to the invention of claim 2, the control at the time of failing is made easier, and the control unit having high credibility can be provided by using the driving cylinder as a reciprocating drive means.
The invention of claim 3 is the control unit of the machine tool as set forth in claim 1, wherein said reciprocating drive means has a member, being free to drive and move within a predetermined stroke, and said sensor detects movement of said member so as to detect release of a state of said workpiece being fixed and held with said workpiece holding members.
According to the invention of claim 3, the sensor detects the movement of the member of the reciprocating drive means, being free to drive and move within a predetermined stroke, thereby detecting the release of a state of the workpiece being fixed and held with the workpiece holding members. Then, the release of the state of being fixed and held can be easily detected.
The invention of claim 4 is the control unit of the machine tool as set forth in claim 1, wherein interlocking drive means of said workpiece holding members is provided between said respective sliding members, and said workpiece holding members of said respective sliding members can be synchronously moved by said interlocking drive means.
According to the invention of claim 4, the workpiece holding members synchronously driven by the interlocking drive means of the workpiece holding member has a danger of simultaneously losing the holding force of the workpiece even at the time of failing. But, proper measure can be taken by the present invention.
The invention of claim 5 is the control unit of the machine tool as set forth in claim 4, wherein said each sliding member is provided with a fluid driving means of said workpiece holding member, and said interlocking drive means has a fluid piping means for connecting said fluid driving means of said respective sliding members.
According to the invention of claim 5, the workpiece holding members communicated and connected by the fluid piping means has a danger of simultaneously losing the holding force of the workpiece at the time of failing when the fluid piping means makes some trouble. But, proper measure can be taken by the present invention.
The invention of claim 6 is the control unit of the machine tool as set forth in claim 3, wherein a position of said workpiece fixed and held with said reciprocating drive means is set at an intermediate position of said predetermined stroke of said reciprocating drive means.
According to the invention of claim 6, the position of the workpiece fixed and held is provided at an intermediate position of the predetermined stroke of the reciprocating drive means. Then, the sliding member can be easily driven in the direction of the axial center by further driving the reciprocating drive means in the direction of the stroke limit of the stroke at the time of failing.
The invention of claim 7 is the control unit of the machine tool as set forth in claim 1, wherein a spindle drive stop control means is provided for at least stopping rotating and driving said spindle when said sensor detects release of a state of said workpiece fixed and held with said workpiece holding members.
According to the invention of claim 7, the spindle drive stop control means can at least stop the rotation and driving of the spindle when the sensor detects the release of the state of the workpiece fixed and held by the workpiece holding members. Then, the spindle is immediately stopped in the state of maintaining the state of holding the workpiece, and it""s safe.